The present invention relates to a sorption process for the separation of components present within a mixture by contacting the mixture with a bed of magnetizable adsorbent particles wherein the adsorbent particles are magnetically stabilized in a stationary fluidized bed and in addition, contacting the adsorbent particles under conditions of simulated counter-current flow. More specifically, this separation process fluidizes the bed of magnetizable adsorbent particles while maintaining the bed in a stationary position and applies a magnetic field to the bed of adsorbent particles at a strength sufficient to suppress solids backmixing and fluid by-passing, and to preserve staging. A continuous process is provided by contacting the feedstream with the adsorbent in a simulated countercurrent flow system wherein the stream flows upwards trough a desorption zone, one or more rectification zones and an adsorption zone, each zone being serially and circularly interconnected and divided into a plurality of serially interconnected sections, each section containing adsorbent with the points of introduction and withdrawal of the streams into and from the sections being simultaneously and periodically shifted to simulate countercurrent flow.
The present sorption process by combining simulated countercurrent flow with a magnetically stabilized fluidized bed process has advantages over either of these processes taken alone. Among the advantages are that axial dispersion in a static (stationary) magnetically stabilized bed appears to be lower than that of a moving magnetically stabilized bed. In addition, since there will be less movement of particles in a static magnetically stabilized bed, there will be less attrition of the particles and therefore less need to replace the particles. Also, since the particles are stationary the uniform dispersion of the particles within the zones will be easier to maintain than in a moving bed configuration, with the uniform dispersion of particles bearing directly on the efficiency of separation achieved. Further, there will be no need to provide transportation systems for removing and introducing the particles continuously into the magnetically stabilized bed as in a moving bed system, thereby saving the capital and energy expenditures associated therewith.
In fixed bed adsorption process, the process is limited by particle size of the adsorbent material due to the high resistance to passage of the fluid through a fixed bed of small particles, while there is no such resistance to fluid throughput for small particles in a fluidized magnetically stabilized bed. Further, since small particles can be used in the present sorption process, separations become more distinct and resultant recoveries and purities are improved. The high resistance to fluid flow through fixed beds of smaller particles will require higher pressure drops across the bed to ensure adequate fluid throughput, thus subjecting the bed to excessive mechanical stress and contributing to attrition of solid particles. Reducing fluid flow through a fixed bed of smaller particles to provide a lower pressure drop across the bed would not be economical, since a low throughput of feed corresponds to a process that is less economical. Another advantage of a fluidized magnetically stabilized bed over a fixed bed is the lack of gravitational stresses on the particles which helps reduce attrition of solids. In addition, the magnetically stabilized bed allows poisoned or otherwise deactivated sorbent to be rapidly replaced with far less shutdown time than is required for fixed beds, since fixed beds generally require careful reloading to avoid channeling of fluid through the bed.
The prior art discloses a number of simulated countercurrent flow systems wherein a continuous process is used in connection with fixed beds by simultaneously and periodically shifting points of introduction and withdrawal of the streams in order to simulate the countercurrent flow of the adsorbent particles and the feed. U.S. Pat. Nos. 2,985,589, 3,040,777, and 3,201,491 disclose the use of such simultaneous and periodic shifting of the feed and withdrawal points, specifically through use of a rotary valve. U.S. Pat. Nos. 3,268,605, 3,268,604 and 4,031,151 also disclose simulated countercurrent flow systems.
Various processes for operating magnetically stabilized fluidized beds for uses such as separations are disclosd in the art, including U.S. Pat. Nos. 4,155,927, 4,247,987, and 4,283,204. However, common to the separation processes disclosed in these patents are that the bed of particles move (e.g. in a plug-flow manner) against the contacting fluid stream creating a countercurrent flow of fluid and particles. This countercurrent flow requires the particles to be removed from the vessel and reintroduced. The present sorption process does not move the particles of the magnetically stabilized fluidized bed, but maintains the particles in a stationary position and utilizes a simulated countercurrent flow system to provide a continuous separation process which maintains the advantages of a continuous process and the advantages of a magnetically stabilized fluidized bed.